1. Field of the Invention
The present invention relates to a cross-coil type indicator. More particularly, the present invention relates to an improvement of the cross-coil type indicator preferably employable for an instrument of the type to be installed on an automotive vehicle, e.g., a speed meter, a rotation meter, a boost meter or the like wherein the indicator includes a movement for rotationally driving a pointer shaft corresponding to a quantity of measurement, a pointer firmly supported by fitting the foremost end part of the pointer shaft into a press-fit hole of the pointer, and a dial plate having a series of calibrations arranged thereon to indicate the present quantity of measurement in cooperation with the pointer.
2. Description of the Related Art
To facilitate understanding of the present invention, a conventional typical cross-coil type indicator will be described below with reference to FIG. 4.
FIG. 4 is a vertical sectional view of the conventional cross-coil type indicator. This indicator is constructed in such a manner that a pair of coils adapted to generate magnetic fields intersecting each other at a right angle are fed with an electric current of which intensity varies corresponding to a quantity of measurement so that a magnet rotor is rotated in the direction of a composite magnetic field derived from combination of the magnetic fields generated by the pair of coils so as to indicate the quantity of measurement in cooperation of a pointer adapted to be rotated by the magnet rotor with the aid of a graduation or scale arranged on a dial plate.
In detail, as shown in FIG. 4, a movement 1 for rotationally driving a pointer shaft 1a corresponding to a quantity of measurement includes a coil bobbin 11, and two coils 12 are arranged around the outer periphery of the coil bobbin 11 in the overlapped state such that they intersect each other at a right angle. A disc-shaped magnet rotor 13 including a south pole and a north pole is rotatably supported in a hollow space 11a of the coil bobbin 11, and a pointer shaft 1a made of a metallic material is fixedly secured to the magnet rotor 13 while extending through the central part of the rotor. The pointer shaft 1a is rotatably supported in the coil bobbin 11 such that its one end, i.e., the upper end of the pointer shaft 1a as seen in the drawing is upwardly projected outside of the coil bobbin 11. As the coils 12 are turned on, the magnet rotor 13 is rotationally driven together with the pointer shaft 1a by a predetermined angle.
A collar 15 for a spiral leaf spring 16 is immovably fitted onto the pointer shaft 1a in such a manner that the inner end of the spiral leaf spring 16 is fixed to the collar 15 and the outer end of the spring is fixed to the coil bobbin 11. While the coils 12 are turned off and the magnet rotor 13 is not rotationally driven, the spiral leaf spring 16 serves to return the pointer shaft 1a to a predetermined zero position with its resilient force.
A dial plate 18 is fixedly mounted on the movement 1 by set screws 19, and the foremost end part of the pointer shaft 1a is projected upward of the dial plate 18 so that a pointer 20 molded of a synthetic resin material is press-fitted onto the pointer shaft la. It should be noted that the foremost end part of the pointer shaft la is slightly tapered so as to enable it to be easily fitted into a press-fit hole 20b formed in a boss 20a of the pointer 20.
In addition, a movement case 21 is arranged outside of the coil bobbin 11 so as to shut the inner and outer magnetic fields.
With the indicator as constructed in the above-described manner, when the pointer 20 is to be fixed fitted onto the foremost end of the pointer shaft 1a, first, the pointer 20 is provisionally fitted to the foremost end of the pointer shaft 1a. While the foregoing state is maintained, each of the coils 12 is then fed with an electric current of which intensity corresponds to a predetermined quantity of measurement. For example, in a case where the indicator is used as a speed meter, each coil 12 is fed with an electric current of which intensity corresponds to a speed of, e.g., 40 km/hr. While the coils 12 are turned on, the position of the pointer 20 is properly adjusted such that the pointer 20 which has been provisionally fitted onto the pointer shaft la assumes an indication position on the dial plate 18 corresponding to the foregoing speed of 40 km/hr. Subsequently, while the foregoing position is maintained, the foremost end of the pointer shaft 1a is forcibly inserted into the press-fit hole 20b by depressing the pointer 20, whereby the pointer 20 is fixedly held at an adequate position.
When the coils 12 are fed with a predetermined intensity of electric current in response to a signal derived from measurement of a vehicle speed or the like, the magnet rotor 13 is rotated by an angle corresponding to a quantity of measurement under the influence of the composite magnetic field induced by the coils 12, causing the pointer 20 to be rotated to a predetermined position on the dial plate 18 via rotation of the pointer shaft 1a. As a result, the present quantity of measurement is visually recognized by reading the graduation on the dial plate 18.
When the coils 12 are turned off, the magnet rotor 13 is rotationally returned to the zero position by the resilient force of the spiral leaf spring 16.
However, with respect to the conventional indicator constructed in the above-described manner, since the foremost end of the pointer shaft 1a is forcibly inserted into the press-fit hole 20b of the pointer 20 by depressing the pointer 20 after the indication position of the pointer 20 to be assumed on the dial plate 18 is visually recognized while the coils 12 are fed with an electric current of which intensity corresponds to a predetermined quantity of measurement, there arises a malfunction that a small amount of relative rotation is caused between the pointer shaft la and the pointer 20 due to slight injury on the outer surface of the pointer shaft 1a or the inner wall surface of the press-fit hole 20b of the pointer 20 or due to slight deformation of the press-fit hole 20b of the pointer 20
Once such a malfunction as mentioned above has arisen, the pointer 20 is fixedly fitted onto the pointer shaft 1a at a position deviated from the predetermined indication position, and there appears a problem that indication properties of the pointer 20 are degraded, resulting in incorrect indication of the present quantity of measurement.